There is a constantly increasing need for sunscreen protection agents in a population that is exposed to an increasing amount of damaging sunlight. The damage can be immediate and long-term, with effects ranging from sunburn, rashes, and cell and tissues damage to premature wrinkling and skin cancer. In this sense, many sunscreening chemicals have been developed in the past protecting against the harmful effect of UV-A and/or UV-B wavelength and even shorter wavelength. These chemicals are usually incorporated either alone or in combination with each other into cosmetic or pharmaceutical preparations which are widely known and used.
Most UV filters used in sunscreen compositions are monomeric compounds having the inherent risk that such compounds can penetrate the skin barrier, which is a highly undesirable effect. Thus, the major drawbacks derived from the use of common sunscreens are adverse reactions comprising cutaneous problems, such as allergic contact reactions, photocontact reactions, and drying or tightening of the skin. Subjective irritation associated with burning or stinging without objective erythema is the most common sensitivity complaint from sunscreens. This irritation is most frequently observed in the eye area. However, persistent objective irritant contact dermatitis is a more common side effect. Individuals with preexisting eczematous conditions have a significant predisposition to sensitization associated with their impaired cutaneous barrier. In addition, certain antibiotics, birth control pills, diuretics, antihistamines and antidepressants are among the commonly used drugs that can increase sensitivity to the sun's rays. Moreover, some of these cutaneous problems are induced by degradation products of the sunscreens formed upon exposure to sunlight. Attempts have been made to solve the risk of skin penetration by encapsulating at least one type of UV filter which is present in a sunscreen formulation. For example, UV filters on the basis of polysiloxanes which may be either linear or cyclic have been described in WO93/04665, WO94/06404, EP538431, EP392883 and EP358584. With these polysiloxanes the risk of skin penetration is lower, but it is sometimes difficult to incorporate the polysiloxanes in sunscreen compositions due to incompatibility problems. Patent application WO2005/053631 refers to microcapsules with UV filter activity, wherein at least one type of crosslinkable chromophore with UV-A and/or UV-B and/or UV-C filter activity, and optionally at least one type of crosslinkable monomer which has no UV-A and/or UV-B and/or UV-C filter activity, are subjected to a crosslinking reaction in the absence of non-crosslinkable chromophores with UV-A and/or UV-B and/or UV-C filter activity. The invention also refers to sunscreen compositions comprising said microcapsules.
The prior art also describes some UV absorbers in the form of particles. In this sense, patent application WO2005/120440 refers to particles comprising an inorganic network and organic compounds covalently bonded to the network via a spacer group, characterised in that the organic compounds are present in the interior of the particles and optionally also on the surface of the particles. The invention also refers to formulations and compositions comprising said particles.
Patent application WO2009/101016 and Walenzyk, T. et al., International Journal of Cosmetic Science (2005), 27(3), 177-189, refer to particles that can be obtained by the reaction of inorganic nanoparticles with organic molecules containing functional groups, and use thereof as UV absorbers in cosmetic or dermatological applications.
Some benzoic acid ester compounds have been discovered and disclosed in WO2006/100225, as well as their uses as photochemical precursors of ultraviolet absorbers, processes, cosmetic or pharmaceutical compositions, personal care compositions, and industrial compositions related thereto. Some silane-functionalized ultraviolet screening agent precursors have also been disclosed in U.S. Pat. No. 4,328,346. These compounds undergo a photochemical transformation in the presence of sunlight that enhances their UV screening ability.
Document WO2011/045389 describes some silyl polymeric benzoic acid esters compounds in the form of particles having an increased photostability and increased persistence on the skin as they have the relevant physical property of being essentially hermetic, thus avoiding the release of benzoic acid ester compounds and its phototransformation products, endowing with a safer profile both for sunscreen user and for the environment. However, the rate of conversion under the typical light doses under real solar irradiation conditions was not fast enough to provide the best protection to the users. In addition, the synthesis of some of these compounds required the use of harmful starting compounds, as well as expensive and long-lasting purification steps, and the yield is not good enough to allow the production thereof on an industrial scale. On top of that, the presence of standard UV filters in the sunscreen formulation resulted in low conversions for these compounds, which further detracted from their protection efficiency.
Thus, it is desirable to develop new sunscreen compounds with higher UV screening ability, faster conversion rates, ability to convert in the presence of additional UV filters, and that can be obtained by cost-effective and easier synthetic routes.